lol, this will be messy.
Look and see if both your names are on the lease. If just your name no problem.
If both, then you're equal cotenants, and you'll need to draw up a contract or talk to leasing office and get them to give you a contract for her to sign to seperate you from the lease agreement or since you want to stay, state that she's a sub tenant and then you can request she leave.
If the lease says, she's the subtenant then you can ask her to leave., evict her.